1. Field of the Invention
The subject matter of the present invention is a microemulsion, which is usable, especially as a cosmetic, dermatological or pharmaceutical agent for skin or hair treatment, preferably in the form of an optically clear, transparent or at least translucent product. This microemulsion contains water, an oil phase comprising liquid hydrophobic oils and an emulsifier mixture of at least two selected emulsifiers.
2. Related Art
Microemulsions are macroscopially homogeneous, optically transparent, low viscosity, thermodynamically stable mixtures comprising two non-miscible liquids and at least one nonionic or ionic surfactant, which contain two hydrophobic groups. If an ionic surfactant containing only one hydrophobic group is added to both components, which are insoluble in each other, e.g. water and nonpolar hydrocarbon, a co-surfactant, usually a short chain aliphatic alcohol, is needed to form a microemulsion. A microemulsion is a ternary mixture of water, hydrophobic phase and surfactant phase. Microemulsions have been shown to be structured with submicroscopic strongly fluctuating bi-continuous oil and water domains with a transmission electron microscope. The sizes of the domains between 3 and 100 nm are stabilized by the boundary surface tension between water-rich and oil-rich phases in the presence of a saturated monomolecular surfactant layer. Frequently microemulsions are solid or semi-solid and have a behavior known as the “ringing effect”. Many pharmaceutical and cosmetic preparations are microemulsions. A general problem with microemulsions is that they have a high risk of skin incompatibility, especially skin and eye irritation, in comparison to normal (macro)-emulsions built up from the same recognized safe ingredients. The problem with using especially mild and skin friendly surfactants is that they do not provide sufficient stability and turbidity, separation or color changes can occur. Alternatively the desired hardness or solidity of the product may change or degrade with time.